Media advocacy groups say the Internet is becoming the new battleground for press freedom as authoritarian governments around the world crack down on growing expressions of dissent on the web.

From China to Iran, bloggers have provided voices of dissent in places where few, if any, were heard before.

But a group of U.S. congressmen and press freedom activists are drawing attention to the growing censorship of online journalism around the world.

Committee to Protect Journalists Deputy Director Robert Mahoney says bloggers are often more vulnerable than traditional journalists.

"Whereas in the past journalists worked usually for a newspaper or a broadcasting company and had some kind of institutional-corporate protection, they had colleagues and on staff they had lawyers who could help them when they got into trouble - now more and more of these bloggers are independent, freelancers even, they have no backing, they are on their own when their up against these huge oppressive government bureaucracies," Mahoney said.

The Committee to Protect Journalists says last year it found at least 68 bloggers, Web-based reporters and online editors under arrest worldwide. That was half the total number of journalists in jail.

Journalism groups worry that even those who are not jailed may be censoring themselves as a consequence of the crackdowns.

Iranian blogger Omid Memarian was imprisoned in 2004 for his work as a journalist. He later left Iran and monitored the bloody repression of street protests that followed the elections in June 2009.

"If it was not for the Internet, God knows how many more people would have been killed on the streets of Tehran and other cities," Memarian said.

The Internet is being used to expose torture, organize public protests, and push the limits of acceptable speech in repressive societies.

Blogging has taken off in China in recent years. Tienchi Martin-Liao of the Independent Chinese PEN center estimates there are now tens of millions of bloggers. But the government is using technology developed in the West to monitor everything from e-mail to voice over the internet.

She said Western companies should follow Google's lead and stop cooperating with the Chinese government.

"Do they want do the evil and make their business, or do they also want to make their contribution to try to help this country out of this dilemma, out of this controlling system," asked Martin-Liao.

Freedom of speech activists say there is an increasing arsenal of software that helps online journalists circumvent attempts at censorship. But countries like Iran and China have become increasingly sophisticated at using technology and blogging propaganda.